Generally, this type of engine comprises a combustion chamber within which a fuel mixture undergoes a compression phase, followed by a combustion phase under the effect of spark ignition means, such as a plug.
It has been observed that this fuel mixture can follow an abnormal combustion that generates mechanical and/or thermal stresses some of which can seriously damage the engine.
This abnormal combustion is essentially due to a pre-ignition (or self-ignition) of the fuel mixture before the plug initiates ignition of the mixture present in the combustion chamber.
In fact, considering the high pressures and the high temperatures reached in this combustion chamber as a result of supercharging, combustion start can occur sporadically well before the time when ignition of the fuel mixture by the plug occurs.
In cases where this abnormal combustion due to pre-ignition or self-ignition occurs suddenly, in a random and sporadic manner, it is referred to as rumble.
The latter abnormal combustion leads to very high pressure levels (of the order of 120 to 250 bars) and to a thermal transfer increase that may cause partial or total destruction of the moving elements of the engine, such as the piston or the piston rod.
Furthermore, it has been observed that this abnormal combustion takes place at high loads and generally at low engine speeds.
More precisely, this abnormal combustion appears when an ignition sub-advance is achieved as a result of circumstances linked with incipient engine knock, a phenomenon that then requires to decrease this advance and thus to increase rumble risks at low engine speed.
One solution for preventing this risk consists in limiting the maximum cylinder pressure angle so as to avoid generating temperature and pressure conditions favouring such rumble.
This solution involves the drawback of not allowing to exploit all of the performance potential of this spark-ignition engine. In fact, the load increase via the supercharging pressure generates engine knock, which requires application of a conventional ignition sub-advance. This sub-advance moves forward the combustion and therefore the maximum cylinder pressure angle that must be limited to a usual value of 35° crank angle after the TDC (combustion Top Dead Centre). The maximum performances of the engine at low speed are thus limited to the load for which the ignition advance adjustment corresponds to these two combined criteria.
The present invention thus aims to overcome the aforementioned drawbacks by means of a combustion method allowing rumble appearance risks to be limited.